Current limiting circuit breakers, wherein the circuit breaker contact arms are arranged to separate independently from the circuit breaker operating mechanism, provide for rapid interruption of current within the first half cycle of the current waveform. U.S. Pat. No. 4,375,021 in the names of F. Pardini et al. describes a current limiting circuit breaker which employs a magnet motor to increase the rate at which the contacts become separated. In order to extinguish the arc that occurs between the contacts, a unique arc chute arrangement multi-functionally motors the arc as well as providing gases to enhance the arc extinction process. The movable contact arms described within the Pardini et al. patent both carry the current under quiescent steady state conditions as well as becoming separated under heavy overload conditions. To prevent undue heating of the contacts and the contact arms under such steady state conditions, the contacts are held together by substantial holding forces applied to the arms and the arms are fabricated from heavy copper bar stock to provide the required conductivity while maintaining a relatively low temperature. The heavy movable contact arms, in turn, require substantial magnetic forces to overcome the holding forces and to rapidly move the arms to the open position. For higher rated current limiting breakers, the movable contact arms, contacts and magnetic forces must be increased in size to handle the larger current ratings.
This invention proposes a current limiting circuit interrupter of reduced size by employing a separate pair of fast opening bridging contacts for handling the steady state or quiescent current on a continuous basis and a pair of movable contact arms of reduced size for magnetic repulsion upon overload.
U.S. Patent Application Ser. No. 610,947 in the name of E. K. Howell entitled "Solid State Circuit Interrupter" describes a solid state circuit interrupter wherein circuit interruption is obtained by a pair of contacts in parallel with a solid state switch such that the separating contacts do not produce an arc upon separation. No arc chute or other arc extinguishing means is required with the Howell solid state circuit interrupter. It has been discovered that a hybrid current limiting circuit interrupter combining the fast opening bridging contacts with the solid state switch provides a current limiting circuit interrupter of further reduced size by eliminating the arc chute.
U.S. Patent Application Ser. No. 665,841 also in the name of E. K. Howell entitled "Fault Current Interrupter" describes a circuit interrupter wherein circuit interruption is provided by means of a pair of contacts connected in parallel with a positive temperature coefficient resistor and a voltage dependent resistor. The current first transfers from the contacts immediately upon separation, through the positive temperature coefficient resistor and then through the voltage dependent resistor to interrupt the current. The bridging contacts of the instant invention can also be used with the positive temperature coefficient resistor and voltage dependent resistor for even faster circuit interruption. Both of the aforementioned U.S. Patent Applications are integrated herein for reference purposes.